Typical examples of a commercially available soft lens for eye include a soft contact lens. A hydrogel material having a water content of about 25 to 80% is commonly used in the commercially available soft contact lens. However, since the low water content soft contact lens made of the hydrogel material contains water, there arises a phenomenon in which water is vaporized from the contact lens. Thereby, certain fixed proportions of contact lens wearers feel dry more strongly as compared with the case of the naked eye, and thus feel uncomfortable. Among these contact lens wearers, some persons complain about a condition of so-called contact lens-related dry eye. Since a water-containing soft contact lens made of a hydrogel material is likely to be contaminated with components in a lacrimal fluid and also contains a large amount of water, there was also a risk of the growth of bacteria.
There has been known as, a highly oxygen permeable low water content soft contact lens, for example, a silicone rubber lens obtained by a method of adding a platinum-based catalyst to a mixture of polydimethylsiloxane in which both ends of the molecular chain are blocked with a vinylmethylsilyl group, and methyl hydrogen polysiloxane, followed by heat-curing using a molding method (Patent Literature 1). Patent Literatures 2 to 6 disclose a highly oxygen permeable contact lens material composed mainly of polysiloxane having a plurality of polymerizable functional groups.
Patent Literature 6 discloses a contact lens material made of a polymer obtained by polymerizing a difunctional organosiloxane macromer alone, or a polymer obtained by copolymerizing a difunctional organosiloxane macromer with the other monomers, and also discloses, as a monomer to be used in copolymerization, an acrylic acid fluoroalkyl ester or a methacrylic acid fluoroalkyl ester, and an acrylic acid alkyl ester or a methacrylic acid alkyl ester.
However, the following problems also lie in a conventional highly oxygen permeable low water content soft contact lens. First, a silicone rubber lens has such a drawback that a hydrophilized layer formed so as to improve hydrophobicity of the surface of the lens is peeled, or adhesion of the lens to the cornea occurs due to too large resilience, and thus the silicone rubber lens had not widely been put into practice.
A material composed mainly of polysiloxane having a plurality of polymerizable functional groups has high oxygen permeability and also has flexibility, and the material is considered to be one of materials which are suitable for a contact lens. However, since tackiness is left on the surface of the lens after polymerization, the lens may adhere to the cornea and is also insufficient in balance between flexibility of the lens and mechanical properties such as folding resistance.
There have been known various methods for modification of a surface of a soft lens for eye. Among these methods, there is known a method in which layers of two or more kinds of polymer materials are coated and accumulated in a layer by layer fashion (Patent Literatures 7 to 9). Among these methods, a method of alternately forming layers made of two polymer materials, each having an opposite electric charge, in a layer by layer fashion by coating is called an LbL method, and it is considered that each layer of the material is noncovalently bonded to the other layer made of a different material. However, the highly oxygen permeable soft lens for eye in which utility of this method is clearly shown is made only of a silicone hydrogel material, and utility to the low water content soft lens for eye has not been known. Conventional LbL coating was carried out to obtain a multi-layered structure constituted from about 4 to 20 layers, and thus the production process may increase, to cause an increase in production costs.